Growing racial and ethnic differences in the prevalence of obesity and the diseases and deaths due to obesity are a serious public health concern. The National Institutes of Health have highlighted the need to reduce and eventually eliminate these troubling disparities. The highest rates of obesity and physical inactivity (IA) occur among the most disadvantaged populations-racial and ethnic minorities and those with the highest poverty rates and least education, measures traditionally used to indicate social disadvantage. The goal of this research is to examine the impact of social disadvantage in adolescence on longitudinal patterns of obesity and IA across the transition to young adulthood, a period when adult lifestyle behaviors are solidified and major racial/ethnic differences in obesity become apparent. The life course and ecological model are utilized as overarching theoretical frameworks to guide the conceptualization of dynamic and comprehensive mechanisms of social disadvantage that link race/ethnicity and low socioeconomic status (SES) to obesity and IA. Data from three waves (Wl:1995, Wll:1996, Wll:2002) of the National Longitudinal Study of Adolescent Health are used to track obesity and IA trajectories from adolescence (Wll: ages 13-19 y.) into adulthood (Will: ages 18-26 y.) and to measure factors at the individual, family, peer, school and neighborhood level in adolescence (Wl and Wll) that shape these trajectories. The three aims of the proposed research investigate the role of social disadvantage in the social contexts of young people's lives and determine if they serve as mechanisms through which race/ethnic and SES disparities operate. These mechanisms include: (1) cumulative risk (CR) indices, which refers to the number of risk factors that exists in a child's social environment with the assumption that disadvantage is related to the accumulation of risk factors rather than a singular exposure; (2) Multilevel socioeconomic disadvantage-disadvantage present in the peer, school, and neighborhood context (e.g., proportion of peers/school/neighborhood with parents who have no high school diploma) and (3) parenting styles and practices. After adequately creating rich and parsimonious measures, multilevel models will be employed to assess the unique influence of each level of disadvantage on the risk of obesity in adolescence and adulthood. Multivariate logistic regression models will be employed to determine if CR indices and parenting behaviors mediate the relationship between race/ethnicity (and low SES) and obesity and IA trajectories in samples divided by sex. By identifying alterable mechanisms operating in the social environments of disadvantaged populations that produce obesity and IA disparities, this research can inform interventions aimed at eliminating them. [unreadable] [unreadable] [unreadable] [unreadable]